This application claims priority to German Application 100 43 238.7, filed on Sep. 2, 2000, the teachings of which are incorporated herein by reference.
Devices for casting mouldings made from wax are known, for example from U.S. Pat. No. 4,934,921. Wax is conveyed from a plastifying unit by means of a piston into an injection unit and supplied to the moulding nest. Plastifying and injecting units, which are provided with means for cooling, are known, for example, from U.S. Pat. No. 3,588,956, since, for example, in PVC processing, precise temperature control is required.
For some manufacturing tasks, it is advantageous to have precise shaped wax mouldings, which serve as a core or casting mould which can be melted out, for example, within the framework of a casting process.
Wax may be processed in principle in an injection-moulding machine. However, it has been shown that in classical use of an injection-moulding machine, problems occur during wax processing. The result is namely then that the wax sticks in the thread region of the plastifying and injecting screw, so that the spirals become more and more clogged and become inefficient to use. The accumulation of wax may also take place disadvantageously even at other points of the injection-moulding machine, for example, in the region in front of the die. An already advantageously designed device is proposed in German Offenlegungsschrift No. 19 824 129. Tests using such devices have shown that the wax starts to melt even in the feed funnel due to the temperature prevailing in the injection cylinder and hence tends to stick.
Prior cooling of the wax granules has led to the surprising result that the disadvantages described no longer occur.
One aspect of the present invention is therefore to provide a device and a process for cooling granules, which facilitates relatively problem-free processing of the granules, in particular wax granules, in otherwise conventional injection-moulding machines.
In one embodiment, a device is provided which cools the granules, in particular wax granules, before supplying them to the injection-moulding machine, by arranging the outlet opening directly or indirectly at a feed region of the screw of an injection-moulding machine and the cavity is connected to a cold-gas production device.
This ensures that the granules may be cooled to about 4xc2x0 C. before being supplied to the injection-moulding machine. Sticking, for example, of the grains of wax granules is thus minimized. Any size of granules can be used. The walls of the cavity, in one embodiment, are advantageously insulated to improve the cooling effect.
The air supply, in one embodiment, is arranged in the lower region of the cavity, that is, in the vicinity of the outlet opening, and the air discharge is arranged in the upper region, that is, in the vicinity of the inlet opening. The cooled air is thus forcibly guided through the granules.
By way of further development, the cold-gas production device can be equipped with a heat exchanger. It is advantageous if a water separator is additionally arranged in the pipes and hence in the air circuit. Moisture is removed from the air by this water separator; that is, not only cold, but also dry air is conveyed through the granules, which results in drying of the granules and has a positive effect on the following processing method.
As an alternative, it is also conceivable to modify a commercially available refrigerated cabinet such that the granules are stored therein and may be drawn off by suction and supplied to the machine as required.
The process of the invention for cooling granules is provided wherein the inlet temperature and the outlet temperature of the gas is determined, and by determining the temperature difference, the preset theoretical temperature in the cavity is controlled and/or regulated. The preset theoretical temperature advantageously lies below the room temperature.
By way of further development, water is removed from the gas before supplying it to the cavity by means of a drying device, for example, by a water separator. Drying of the granules is thus achieved at the same time, since the gas may take up moisture when flowing through the cavity filled with granules.
It is particularly economical if the gas discharged from the cavity is supplied back to the cold-gas production device and thus passes through the device in a circuit. Air is used primarily as gaseous medium, but it is also conceivable to use, for example, nitrogen or other gases.